Internal combustion engines are ever more commonly being equipped with supercharging, wherein supercharging is primarily a method for increasing power, in which the charge air required for the combustion process in the engine is compressed, as a result of which a greater mass of charge air can be supplied to each cylinder per working cycle. In this way, the fuel mass and therefore the mean effective pressure can be increased.
It is preferable for a charge-air cooler to be provided in the intake line, by means of which the charge air is cooled before it enters the at least one cylinder. The cooler lowers the temperature and thereby increases the density of the charge air, such that the cooler also contributes to improved charging of the at least one cylinder, that is to say to a greater air mass. In effect, compression by cooling takes place.
If the internal combustion engine is equipped with an exhaust-gas recirculation (EGR) system, the exhaust gas recirculated by means of EGR to the inlet side is mixed with fresh intake air and the mixture of fresh air and recirculated exhaust gas produced in this way forms the charge air, which is then if appropriate supplied to the charge-air cooler for cooling. Recirculated exhaust gas may basically be introduced into the at least one intake line of the intake system upstream or downstream of the charge-air cooler.
It is not the aim to extract the greatest possible amount of heat from the charge air by means of charge-air cooling continuously, that is to say under all operating conditions of the internal combustion engine. In fact, demand-dependent control of the charge-air cooling is sought which allows for the different operating modes of an internal combustion engine and which takes into consideration that it may be advantageous to supply non-cooled charge air to the internal combustion engine, for example in the warm-up phase of the internal combustion engine or during the regeneration of a particle filter provided at the outlet side in the exhaust system. It is assumed here that an increase in the temperature of the charge air and therefore of the cylinder fresh charge likewise increases the exhaust-gas temperature.
To be able to bypass the charge-air cooler, that is to say to be able to conduct the charge air past the charge-air cooler, a bypass line is provided which branches off from the at least one intake line upstream of the charge-air cooler and which opens into the at least one intake line again downstream of the charge-air cooler. A device is required for controlling the charge-air flows conducted via the charge-air cooler and via the bypass line.
According to previous systems, it is possible to arrange in the bypass line a preferably continuously adjustable shut-off element by means of which the bypass line is opened up or shut off to a greater or lesser extent, whereby the flow resistance posed to the charge-air flow by the bypass line is varied and set.
When the bypass line is closed, that is to say shut off, all of the charge air flows through the charge-air cooler. If in contrast the bypass line is opened to a greater or lesser extent, the charge-air flow is split up, with only a part of the charge-air flow passing through the charge-air cooler and the remaining charge-air flow being conducted past the charge-air cooler via the bypass line. Here, the magnitude of the two partial flows is dependent on the position of the shut-off element provided in the bypass line.
The above-described concept for controlling the charge-air cooling makes it possible for the bypass line to be opened up when the shut-off element is open and shut off by moving the shut-off element into the closed position.
In contrast, the intake line leading through the charge-air cooler is always open, that is to say is continuously open, and also cannot be varied in terms of its flow cross section. The charge-air cooler therefore cannot be fully deactivated, such that always a part of the charge-air flow passes through the charge-air cooler. This fact has two disadvantageous effects. Firstly, a part of the charge-air flow is always cooled, even when only non-cooled charge air is supposed to be supplied to the internal combustion engine. Secondly, even after the internal combustion engine is shut down, charge air is supplied to the at least one cylinder via the intake line or intake system owing to the suction effect of the at least one running-down piston. The latter situation causes shuddering of the internal combustion engine owing to the running-down process, which lasts several working cycles.
The inventor herein has recognized the above issues and provides an approach to at least partly address them. In one embodiment, a method for operating an internal combustion engine having at least one cylinder, at least one intake line for supplying charge air to the at least one cylinder, and a device for controlling charge-air flows conducted via a charge-air cooler and via a bypass line around the charge-air cooler, comprises controlling the charge-air flows using the device, the device including a two-stage switchable shut-off element and a continuously adjustable shut-off element, wherein the two-stage switchable shut-off element, which is arranged parallel to the bypass line in the at least one intake line, is switched between an open position and a closed position, and the bypass line is opened up or shut off to a greater or lesser extent by the shut-off element which is continuously adjustable between an open position and a closed position.
In this way, the intake air may be routed to the engine fully via the charge air cooler, partially via the charge air cooler, or without passing through the charge air cooler, depending on desired intake air cooling. Further, by closing both shut-off elements, intake air may be prevented from reaching the engine, with which shuddering of the internal combustion engine as it is shut down is prevented.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.